Stormwater Requirements Worksheet

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					Arlington County Chesapeake Bay Preservation Ordinance Stormwater Requirements Worksheet
Step 1. Enter site characteristics and determine impact area                                                                                                     Arlington County
                                                          Area (sf)                          %I                                                    Chesapeake Bay Preservation Ordinance
Total Site Area                                                        43560                                                                        Stormwater Requirements Worksheet
Existing Impervious Cover                                              20000                          45.9%                                                 Version 2.0 October 2011
Proposed Impervious Cover                                              30000                          68.9%                                       Applicant:

Average Land Cover condition                                            6970                          16.0%
90% of Existing Impervious Cover                                       18000                          41.3%
                                                                                                                            Impact area (sf)
                                                pre<=avg; post<=avg             No                               --
                                                pre<=avg; post>avg              No                               --
                                                pre>avg                         Yes                                                     12000
                                                                                       Total Impact Area                                12000
                                                                   Impact area > 50% of total impervious area?                             No
                                                                             Impact Area Requirement                                    12000
Maximum Watershed Management Fund fee                                           $                      2.50       $                    30,000

Step 2. Vehicle-related pavement treatment
                                                          Area (sf)
Vehicle-related pavement
                      Required to be treated                           0
        Required min. treatment efficiency                           50%
                Treatment credit needed                                0        Not to exceed Impact Area Requirement
                                                     Impervious area
Pervious surface BMPs                                 reduction (sf)                                                  Treatment Credit (sf)
                 Pervious paving system                                                                                                       0
                                                Impervious area treated
                                                         (sf)                     Treatment efficiency                Treatment Credit (sf)
            Additional BMPs                                  (A)                             (B)                             (A X B)
                                                                                                        50%                                   0
                                                                                                                                              0 Is vehicular treatment requirement met?
Total vehicle-related pavement stormwater treatment credits                                                                                   0 YES

Step 3. Additional treatment
                                                     Impervious area
        Pervious surface BMPs                         reduction (sf)                                                  Treatment Credit (sf)
                 Pervious paving system                                                                                                       0
                                                                                                                                                     Are a minimum of 50% of the treatment credits
                  Vegetated roof system                                                                                                       0      obtained through the use of BMPs that provide
                                                Impervious area treated                                                                              annual runoff volume reduction (RR) as detailed in
                                                         (sf)                     Treatment efficiency                Treatment Credit (sf)          the most recent version of the Virginia DCR
            Additional BMPs                                  (A)                             (B)                             (A X B)                 Stormwater Design Specifications?

                                                                                                        50%                                   0
                                                                                                                                              0 Runoff Reduction (RR) BMPs                                credit
                                                                                                                                              0 Rooftop disconnection
Total additional treatment credits                                                                                                            0 Vegetated roof                                                    0
                                                                                                                                                  Rainwater harvesting
Step 4. Determine compliance                                                                                                                      Permeable pavement                                              0
                                                          Area (sf)                                                                               Infiltration
Impact area                                                            12000                                                                      Bioretention
Total treatment credits                                                     0                                                                     Total                                                           0
Remaining impact area                                                  12000                                                                      Percent of total treatment credits                         #DIV/0!
Total Watershed Management Fund fee $                                 30,000 Fee payment only allowed if exception criteria met **                Requirement met?                                           #DIV/0!

 1. At least 50 percent of required treatment credits must come from 'runoff reduction' BMPs?

 2. More than 80% of the post-development impervious area must be treated by BMPs with a least a 50% treatment efficiency

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